This invention relates to a magnetic tape cassette used for a video tape recorder or the like, and more particularly to a magnetic tape cassette including an openable dust cover or front lid for covering the front portion of a cassette casing to protect a magnetic tape when it is out of use.
A magnetic tape cassette which has been conventionally used for a cassette driving device such as a video tape recorder or the like typically includes a front lid openably arranged at the front portion of a casing so as to serve as a dust cover for covering a front opening formed at the front portion of the casing when it is out of use, resulting in preventing entry of dust through the opening into the casing, damage of a magnetic tape and the like.
Now, such a conventional magnetic tape cassette will be described hereinafter with reference to FIGS. 1A to 1G.
The conventional magnetic tape cassette, as shown in FIGS. 1A to 1C, includes a front lid 100 pivotally mounted on the front portion of a casing 102 through support pins 104 so as to be pivotally moved about the pins 104 and constantly biased in the direction of opening the front lid 100 covering an opening formed at the front portion of the casing 102 by means of a bias member (not shown). The cassette also includes a lock lever 106 which is arranged in the casing 102 and adapted to be engaged with the front lid 100 to shut the opening of the casing 102. The lock lever 106 includes a push button or projection 108 projectably fitted in an aperture or through-hole 110 of the casing 102 and constantly biased in the direction of outward projecting from the casing 102 by means of a spring 112 arranged in the casing 102 and a lock pawl 114 adapted to be engaged with a stopper 116 provided on the inside of the front lid 100 to keep the front opening of the casing 102 closed with the front lid 100 when the cassette is out of use.
When opening the front lid 100, force F, as shown in FIG. 1D, is applied to the center of the projection 108 to inward push the projection 108 in the axial direction thereof, resulting in the lock lever 106 being inwardly pushed while it is desired to keep it parallel to the casing 102. This leads to disengagement of the lock pawl 114 of the lock lever 106 from the stopper 116 of the front lid 100, to thereby permit the front lid 100 to be ready to be opened by means of an opening mechanism of a cassette driving device such as a video tape recorder or the like.
Unfortunately, in the conventional magnetic tape cassette constructed as described above, the spring 112 is arranged at the same position as the projection 108 or on the rear side of the projection 108 in a manner to be substantially coaxial with the projection 108, as shown in FIGS. 1B and 1C. Accordingly, when the opening mechanism of the cassette driving device inward pushes the projection 108, it often applies force F to the projection 108 while deviating from the center of the projection 108 or in a manner to be directed obliquely with respect to the axial direction of the projection 108, so that the force deviates from the axis of the spring 112 to cause it to be compressed in a wrong posture. This causes the projection 108 to be forced into the casing 100 in a wrong posture as shown in FIG. 1E or 1F, to thereby fail to release the lock pawl 114 from the stopper 116. This fails to properly operate the front lid 100 and often leads to damage of the cassette.
Accordingly, it would be highly desirable to develop a magnetic tape cassette which is capable of safely and positively accomplishing rapid release of a front lid from a casing when it is desired to open the front lid.